This invention relates to computer-aided design (CAD) systems, and in particular to a method and apparatus for providing surface detail in a two-dimensional design system. The present invention has specific applications to the apparel, footwear and interior design industries.
In the field of computer-aided design, one of the objectives of any CAD system is to display a realistic image of the object displayed on the graphic visual output device, e.g., the cathode ray terminal ("CRT") of the system. A technique for enhancing the realism of the generated image is the addition of surface detail for areas making up the image using texture mapping techniques. Such texture mapping techniques have been employed in three-dimensional ("3-D") CAD systems, notably those used in making animated films. A technique for producing a realistic image of a three-dimensional object in a two-dimensional ("2-D") CAD system and applying surface detail to the image is disclosed in the Edward K. Falk, U.S. Pat. No. 4,888,713 for a SURFACE DETAIL MAPPING SYSTEM, issued Dec. 19, 1989, and assigned to the assignee of the present application. The Falk application discloses a system in which a 2-D image is created in a computer through use of an input device, such as a frame buffer capture camera or digitizing scanner, or created by the user through the use of other image design software tools, such as conventional "paintbox" programs. Tools are provided to define segments of an image and to generate and modify a mesh in segments or portions of segments to allow the designer to create a 3-D appearance to the image. The system disclosed in the Falk patent further stores an array of pixels representing a desired surface detail, such as a fabric pattern, or the like. Means are provided for calculating for each pixel in the image the coordinates of the corresponding surface detail pixel based on the location of the image pixel in the grid and the position of the grid in the mesh. Means are provided for mapping the coordinates for each image pixel to the array of pixels representing the surface detail and for selecting the corresponding pixel in order to generate a graphic visual image of the 2-D image with surface detail applied.
In applying surface detail to a 2-D image of a 3-D object, distortions in fitting the pattern to the image causes pixel compression to occur where more than one pattern pixel maps to an image pixel and pixel "dropout" to occur where no pattern pixel exists for an image pixel. Conventional techniques compensate for pixel compression and pixel "dropouts" in mapping systems by applying bi-linear interpolation during mapping. It is also known that the shading and texture of the original image may be preserved notwithstanding the application of the surface detail by converting the image and surface detail pixel data from (R,G,B) parameters to (H,S,V) parameters, selecting the H and S components from the surface detail pixel data, multiplying the V parameters of the image and surface detail pixel data and dividing by 256 to obtain a composite (H,S,V) parameter for the new image pixel. The (H,S,V) parameters are subsequently converted to (R,G,B) parameters for the new image pixel.
While the invention set forth in the Falk application provided for the first time a technique, for use in a 2-D CAD system, of selectively applying alternate surface detail, or patterns, stored in the computer memory to an image in order to create the appearance of a 3-D object, the system requires on the order of two minutes of time to perform the surface detail mapping process. The system is, thus, impractical for use as a sales tool to, for example, illustrate to a consumer the appearance of an upholstered furniture item in which various fabric designs may be selectively applied. The length of the mapping process interrupts the rhythm of the presentation by the sales person. Additionally, the length of the mapping process impedes the effectiveness of the Falk system as a design tool in the hands of an experienced designer.